Generally, the blue, green and red bands of multispectral satellite sensors do not cover the whole blue, green and red wavelength ranges, respectively. As a result, the “natural” colour composites from the blue, green and red bands do not reproduce natural colours as found in the nature or on a colour photo. Such colour is near natural colour, but still noticeably unnatural. In order to achieve a better visual effect, it is useful to adjust, either manually or automatically, the near natural colour to a more natural colour. Such a colour adjustment is useful in many applications, such as colour image mapping, GIS integration, image visualization, and other purposes.
The most representative ground covers on the Earth's surface are vegetation, water and soil (e.g., surface not covered by vegetation or water). Their general spectral reflectance in different spectral ranges is characterized in FIG. 1. Vegetation curves have a peak in the green range compared to the blue and red ranges. The spectral curves of soil reflectance rise proportional to the wavelength. However, the curve of clear water usually has a peak in blue range and then descends proportional to the wavelength. Therefore, when the blue, green and red bands of a multispectral sensor are displayed with blue, green and red colour, a near natural colour composite can be generated with water shown in blue, vegetation shown in green and soil shown in light yellow grey or light red grey). But, the colour of vegetation often does not show up as a natural green. This makes colour composites look unnatural and not visually pleasing.